Kinetic and thermodynamic investigation of Arthrospira (Spirulina) platensis fed-batch cultivation in a tubular photobioreactor using urea as nitrogen source

BACKGROUND: Fed-batch culture allows the cultivation of Arthrospira platensis using urea as nitrogen source. Tubular photobioreactors substantially increase cell growth, but the successful use of this cheap nitrogen source requires a knowledge of the kinetic and thermodynamic parameters of the process. This work aims at identifying the effect of two independent variables, temperature (T) and urea daily molar flow-rate (U), on cell growth, biomass composition and thermodynamic parameters involved in this photosynthetic cultivation. RESULTS: The optimal values obtained were T = 32 degrees C and U = 1.16 mmol L-1 d-1, under which the maximum cell concentration was 4186 +/- 39 mg L-1, cell productivity 541 +/- 5 mg L-1 d-1 and yield of biomass on nitrogen 14.3 +/- 0.1 mg mg-1. Applying an Arrhenius-type approach, the thermodynamic parameters of growth (?H* = 98.2 kJ mol-1; ?S* = - 0.020 kJ mol-1 K-1; ?G* = 104.1 kJ mol-1) and its thermal inactivation (Delta H-D(0) =168.9 kJ mol-1; Delta S-D(0) = 0.459 kJ mol-1 K-1; Delta G(D)(0) =31.98 kJ mol-1) were estimated. CONCLUSIONS: To maximize cell growth T and U were simultaneously optimized. Biomass lipid content was not influenced by the experimental conditions, while protein content was dependent on both independent variables. Using urea as nitrogen source prevented the inhibitory effect already observed with ammonium salts. Copyright (c) 2012 Society of Chemical Industry

Effects of photobioreactor configuration, nitrogen source and light intensity on the fed-batch cultivation of Arthrospira (Spirulina) platensis. Bioenergetic aspects

Bioenergetic analysis may be applied in order to predict microbial growth yields, based on the Gibbs energy dissipation and mass conservation principles of the overall growth reaction. The bioenergetics of the photoautotrophic growth of the cyanobacterium Arthrospira (Spirulina) platensis was investigated in different bioreactor configurations (tubular photobioreactor and open ponds) using different nitrogen sources (nitrate and urea) and under different light intensity conditions to determine the best growing conditions in terms of Gibbs energy dissipation, number of photons to sustain cell growth and phototrophic energy yields distribution in relation to the ATP and NADPH formation, and release of heat. Although an increase in the light intensity increased the Gibbs energy dissipated for cell growth and maintenance with both nitrogen sources, it did not exert any appreciable influence on the moles of photons absorbed by the system to produce one C-mol biomass. On the other hand, both bioenergetic parameters were higher in cultures with nitrate than with urea, likely because of the higher energy requirements needed to reduce the former nitrogen source to ammonia. They appreciably increased also when open ponds were substituted by the tubular photobioreactor, where a more efficient light distribution ensured a remarkably higher cell mass concentration. The estimated percentages of the energy absorbed by the cell showed that, compared with nitrate, the use of urea as nitrogen source allowed the system to address higher energy fractions to ATP production and light fixation by the photosynthetic apparatus, as well as a lower fraction released as heat. The best energy yields values on Gibbs energy necessary for cell growth and maintenance were achieved in up to 4-5 days of cultivation, indicating that it would be the optimum range to maintain cell growth. Thanks to this better bioenergetic situation, urea appears to be a quite promising low-cost, alternative nitrogen source for Arthrospira platensis cultures in photobioreactors. (C) 2011 Elsevier Ltd. All rights reserved.

Arthrospira (Spirulina) platensis cultivation in tubular photobioreactor: Use of no-cost CO2 from ethanol fermentation

The present study aimed at evaluating the production of Arthrospira platensis in tubular photobioreactor using CO2 from ethanol fermentation. The results of these cultivations were compared to those obtained using CO2 from cylinder at different protocols of simultaneous ammonium sulfate and sodium nitrate feeding. Maximum cell concentration (X-m), cell productivity (P-x), nitrogen-to-cell conversion factor (Y-X/N), and biomass composition (total lipids and proteins) were selected as responses and evaluated by analysis of variance. The source of CO2 did not exert any significant statistical influence on these responses, which means that the flue gas from ethanol fermentation could successfully be used as a carbon source as well as to control the medium pH, thus contributing to reduce the greenhouse effect. The results taken as a whole demonstrated that the best combination of responses mean values (X-m = 4.543 g L-1; P-x = 0.460 g L-1 d(-1); Y-X/N = 15.6 g g(-1); total lipids = 8.39%; total proteins = 18.7%) was obtained using as nitrogen source a mixture of 25% NaNO3 and 75% (NH4)(2)SO4, both expressed as nitrogen. (C) 2011 Elsevier Ltd. All rights reserved.

Simultaneous use of urea and potassium nitrate for Arthrospira (Spirulina) platensis cultivation

Urea has been considered as a promising alternative nitrogen source for the cultivation of Arthrospira platensis if it is possible to avoid ammonia toxicity; however, this procedure can lead to periods of nitrogen shortage. This study shows that the addition of potassium nitrate, which acts as a nitrogen reservoir, to cultivations carried out with urea in a fed-batch process can increase the maximum cell concentration (Xm) and also cell productivity (PX). Using response surface methodology, the model indicates that the estimated optimum Xm can be achieved with 17.3 mM potassium nitrate and 8.9 mM urea. Under this condition an Xm of 6077 +/- 199 mg/L and a PX of 341.5 +/- 19.1 mg L1day1 were obtained.

Arthrospira platensis biomass with high protein content cultivated in continuous process using urea as nitrogen source

Aims: Arthrospira platensis has been studied for single-cell protein production because of its biomass composition and its ability of growing in alternative media. This work evaluated the effects of different dilution rates (D) and urea concentrations (N0) on A.similar to platensis continuous culture, in terms of growth, kinetic parameters, biomass composition and nitrogen removal. Methods and results: Arthrospira platensis was continuously cultivated in a glass-made vertical column photobioreactor agitated with Rushton turbines. There were used different dilution rates (0.040.44 day-1) and urea concentrations (0.5 and 5 mmol l-1). With N0 = 5 mmol l-1, the maximum steady-state biomass concentration was1415 mg l-1, achieved with D = 0.04 day-1, but the highest protein content (71.9%) was obtained by applying D = 0.12 day-1, attaining a protein productivity of 106.41 mg l-1 day-1. Nitrogen removal reached 99% on steady-state conditions. Conclusions: The best results were achieved by applying N0 = 5 mmol l-1; however, urea led to inhibitory conditions at D = 0.16 day-1, inducing the system wash-out. The agitation afforded satisfactory mixture and did not harm the trichomes structure. Significance and Impact of the Study: These results can enhance the basis for the continuous removal of nitrogenous wastewater pollutants using cyanobacteria, with an easily assembled photobioreactor.

Photosynthetic efficiency and rate of CO2 assimilation by Arthrospira (Spirulina) platensis continuously cultivated in a tubular photobioreactor

Similar to other photosynthetic microorganisms, the cyanobacterium Arthrospira platensis can be used to produce pigments, single cell proteins, fatty acids (which can be used for bioenergy), food and feed supplements, and biofixation of CO2. Cultivation in a specifically designed tubular photobioreactor is suitable for photosynthetic biomass production, because the cultivation area can be reduced by distributing the microbial cells vertically, thus avoiding loss of ammonia and CO2. The aim of this study was to investigate the influence of light intensity and dilution rate on the photosynthetic efficiency and CO2 assimilation efficiency of A. platensis cultured in a tubular photobioreactor in a continuous process. Urea was used as a nitrogen source and CO2 as carbon source and for pH control. Steady-state conditions were achieved in most of the runs, indicating that continuous cultivation of this cyanobacterium in a tubular photobioreactor could be an interesting alternative for the large-scale fixation of CO2 to mitigate the greenhouse effect while producing high protein content biomass.

Oxygen supply in Bacillus thuringiensis fermentations: bringing new insights on their impact on sporulation and delta-endotoxin production

The growth kinetics, sporulation, and toxicity of Bacillus thuringiensis var. israelensis were evaluated through the analysis of batch cultures with different dissolved oxygen (DO) profiles. Firstly, DO was maintained constant at 5%, 20%, or 50% throughout fermentation in order to identify the most suitable one to improve the main process parameters. Higher biomass concentration, cell productivity, and cell yield based on glucose were obtained with 50% DO. The higher aeration level also resulted in higher spore counts and markedly improved the toxic activity of the fermentation broth, which was 9-fold greater than that obtained with 5% DO (LC50 of 39 and 329 mg/L, respectively). Subsequently, using a two-stage oxygen supply strategy, DO was kept at 50% during the vegetative and transition phases until the maximum cell concentration was achieved. Then, DO was changed to 0%, 5%, 20%, or 100% throughout sporulation and cell lysis phases. The interruption of oxygen supply strongly reduced the spore production and thoroughly repressed the toxin synthesis. On the contrary, when DO was raised to 100% of saturation, toxic activity increased approximately four times (LC50 of 8.2 mg/L) in comparison with the mean values reached with lower DO levels, even though spore counts were lower than that from the 50% DO assay. When pure oxygen was used instead of normal air, it was possible to obtain 70% of the total biomass concentration achieved in the air assays; however, cultures did not sporulate and the toxin synthesis was consequently suppressed.

Production and characterization of poly-(3-hydroxybutyrate) from recombinant Escherichia coli grown on cheap renewable carbon substrates

Although the biopolymer poly-(3-hydroxybutyrate), P[3HB], presents physicochemical properties that make it an alternative material to conventional plastics, its biotechnological production is quite expensive. As carbon substrates contribute greatly to P[3HB] production cost, the utilization of a cheaper carbon substrate and less demanding micro-organisms should decrease its cost. In the present study a 23 factorial experimental design was applied, aiming to evaluate the effects of using hydrolysed corn starch (HCS) and soybean oil (SBO) as carbon substrates, and cheese whey (CW) supplementation in the mineral medium (MM) on the responses, cell dried weigh (DCW), percentage P[3HB] and mass P[3HB] by recombinant Escherichia coli strains JM101 and DH10B, containing the P[3HB] synthase genes from Cupriavidus necator (ex-Ralstonia eutropha). The analysis of effects indicated that the substrates and the supplement and their interactions had positive effect on CDW. Statistically generated equations showed that, at the highest concentrations of HCS, SO and CW, theoretically it should be possible to produce about 2 g L(1) DCW, accumulating 50% P[3HB], in both strains. To complement this study, the strain that presented the best results was cultivated in MM added to HCS, SBO and CW ( in best composition observed) and complex medium (CM) to compare the obtained P[3HB] in terms of physicochemical parameters. The obtained results showed that the P[3HB] production in MM (1.29 g L(-1)) was approximately 20% lower than in CM (1.63 g L(-1)); however, this difference can be compensated by the lower cost of the MM achieved by the use of cheap renewable carbon sources. Moreover, using differential scanning calorimetry and thermogravimetry analyses, it was observed that the polymer produced in MM was the one which presented physicochemical properties (Tg and Tf) that were more similar to those found in the literature for P[3HB].

Switching the mode of sucrose utilization by Saccharomyces cerevisiae

Abstract Background Overflow metabolism is an undesirable characteristic of aerobic cultures of Saccharomyces cerevisiae during biomass-directed processes. It results from elevated sugar consumption rates that cause a high substrate conversion to ethanol and other bi-products, severely affecting cell physiology, bioprocess performance, and biomass yields. Fed-batch culture, where sucrose consumption rates are controlled by the external addition of sugar aiming at its low concentrations in the fermentor, is the classical bioprocessing alternative to prevent sugar fermentation by yeasts. However, fed-batch fermentations present drawbacks that could be overcome by simpler batch cultures at relatively high (e.g. 20 g/L) initial sugar concentrations. In this study, a S. cerevisiae strain lacking invertase activity was engineered to transport sucrose into the cells through a low-affinity and low-capacity sucrose-H+ symport activity, and the growth kinetics and biomass yields on sucrose analyzed using simple batch cultures. Results We have deleted from the genome of a S. cerevisiae strain lacking invertase the high-affinity sucrose-H+ symporter encoded by the AGT1 gene. This strain could still grow efficiently on sucrose due to a low-affinity and low-capacity sucrose-H+ symport activity mediated by the MALx1 maltose permeases, and its further intracellular hydrolysis by cytoplasmic maltases. Although sucrose consumption by this engineered yeast strain was slower than with the parental yeast strain, the cells grew efficiently on sucrose due to an increased respiration of the carbon source. Consequently, this engineered yeast strain produced less ethanol and 1.5 to 2 times more biomass when cultivated in simple batch mode using 20 g/L sucrose as the carbon source. Conclusion Higher cell densities during batch cultures on 20 g/L sucrose were achieved by using a S. cerevisiae strain engineered in the sucrose uptake system. Such result was accomplished by effectively reducing sucrose uptake by the yeast cells, avoiding overflow metabolism, with the concomitant reduction in ethanol production. The use of this modified yeast strain in simpler batch culture mode can be a viable option to more complicated traditional sucrose-limited fed-batch cultures for biomass-directed processes of S. cerevisiae.

Intestinal IgG uptake by small intestine of goat kid fed goat or lyophilized bovine colostrum

The immunoglobulin G (IgG) uptake and enterocyte nucleus position in the villous were studied in newborn goat kids fed goat or lyophilized bovine colostrum. Two groups of 15 newborn goat kids, each received 5% of body weight of goat colostrum (GC) or lyophilized bovine colostrum (LBC) containing 55 mg/mL of immunoglobulin G (IgG) at 0, 7 and 14 h of life. Three animals were sampled just after birth, receiving no colostrum intake, to be used as control. Samples of duodenum, medium jejunum and ileum were collected at 0, 18, 36 and 96 h of life. IgG vacuoles were not observed in the duodenum throughout the experiment regardless of all the experimental time points. In this segment, at 0, 18 and 36 h of life, nuclei were found in the apical, medial and basal positions in the enterocytes, and localized in the upper, medial and lower parts in the villous, respectively. At 96 h, a basal nuclei position was observed in the enterocytes, throughout the villous. In jejunum, IgG vacuoles were distributed along the villous at 18 and 36 h. In this segment at Oh the nuclei were positioned predominantly apically in the enterocytes, throughout the villous. At 18 and 36 h, no consistent nuclei pattern was verified: however at 96 h, the nuclei were positioned basally in the enterocytes, throughout the jejunal villous. In the ileum at 0, 18 and 36 h, a great number of vacuoles without IgG were verified in the medial-apical part of the villous. In this segment, at Oh of life and 96 h of life, the predominance of basal nuclei was observed. Nuclei were positioned in medial-apically part of the ileal enterocytes in the upper part of the villous at 18 and 36 h. It was found that the jejunal epithelium was the most important segment related to absorption process. The IgG absorption and nucleus position in the newborn goats were dependent on the small intestine segments and experimental time points, regardless of the colostrum source. GC or LCB. Considering the IgG uptake mechanism observed in the present study, the lyophilized bovine colostrum might be used instead of goat colostrum. (C) 2011 Elsevier B.V. All rights reserved.

SYNTHESIS OF N-15-ENRICHED UREA (CO((NH2)-N-15)(2)) FROM (NH3)-N-15, CO, AND S IN A DISCONTINUOUS PROCESS

CO((NH2)-N-15)(2) enriched with the stable isotope N-15 was synthesized based on a reaction involving CO, (NH3)-N-15, and S in the presence of CH3OH. The method differs from the industrial method; a stainless steel reactor internally lined with polytetrafluoroethylene (PTFE) was used in a discontinuous process under low pressure and temperature. The yield of the synthesis was evaluated as a function of the parameters: the amount of reagents, reaction time, addition of H2S, liquid solution and reaction temperature. The results showed that under optimum conditions (1.36, 4.01, and 4.48 g of (NH3)-N-15, CO, and S, respectively, 40 ml CH3OH, 40 mg H2S, 100 degrees C and 120 min of reaction) 1.82 g (yield 76.5%) of the compound was obtained per batch. The synthesized CO((NH2)-N-15)(2) contained 46.2% N, 0.55% biuret, melting point of 132.55 degrees C and did not exhibit isotopic fractionation. The production cost of CO((NH2)-N-15)(2) with 90.0 at. % N-15 was US$ 238.60 per gram.

Hydrogen and Methane Production, Energy Recovery, and Organic Matter Removal from Effluents in a Two-Stage Fermentative Process

This study evaluates the potential for using different effluents for simultaneous H-2 and CH4 production in a two-stage batch fermentation process with mixed microflora. An appreciable amount of H-2 was produced from parboiled rice wastewater (23.9 mL g(-1) chemical oxygen demand [COD]) and vinasse (20.8 mL g(-1) COD), while other effluents supported CH4 generation. The amount of CH4 produced was minimum for sewage (46.3 mL g(-1) COD), followed by parboiled rice wastewater (115.5 mL g(-1) COD) and glycerol (180.1 mL g(-1) COD). The maximum amount of CH4 was observed for vinasse (255.4 mL g(-1) COD). The total energy recovery from vinasse (10.4 kJ g(-1) COD) corresponded to the maximum COD reduction (74.7 %), followed by glycerol (70.38 %, 7.20 kJ g(-1) COD), parboiled rice wastewater (63.91 %, 4.92 kJ g(-1) COD), and sewage (51.11 %, 1.85 kJ g(-1) COD). The relatively high performance of vinasse in such comparisons could be attributed to the elevated concentrations of macronutrients contained in raw vinasse. The observations are based on kinetic parameters of H-2 and CH4 production and global energy recovery of the process. These observations collectively suggest that organic-rich effluents can be deployed for energy recovery with sequential generation of H-2 and CH4.

Feasibility Study of a Solar Reactor for Phenol Treatment by the Photo-Fenton process in Aqueous Solution

Solar reactors can be attractive in photodegradation processes due to lower electrical energy demand. The performance of a solar reactor for two flow configurations, i.e., plug flow and mixed flow, is compared based on experimental results with a pilot-scale solar reactor. Aqueous solutions of phenol were used as a model for industrial wastewater containing organic contaminants. Batch experiments were carried out under clear sky, resulting in removal rates in the range of 96100?%. The dissolved organic carbon removal rate was simulated by an empirical model based on neural networks, which was adjusted to the experimental data, resulting in a correlation coefficient of 0.9856. This approach enabled to estimate effects of process variables which could not be evaluated from the experiments. Simulations with different reactor configurations indicated relevant aspects for the design of solar reactors.

Synthesis of 15N-enriched urea (CO(15NH2)2) from 15NH3, CO, and S in a discontinuous process

CO(15NH2)2 enriched with the stable isotope 15N was synthesized based on a reaction involving CO, 15NH3, and S in the presence of CH3OH. The method differs from the industrial method; a stainless steel reactor internally lined with polytetrafluoroethylene (PTFE) was used in a discontinuous process under low pressure and temperature. The yield of the synthesis was evaluated as a function of the parameters: the amount of reagents, reaction time, addition of H2S, liquid solution and reaction temperature. The results showed that under optimum conditions (1.36, 4.01, and 4.48 g of 15NH3, CO, and S, respectively, 40 ml CH3OH, 40 mg H2S, 100 ºC and 120 min of reaction) 1.82 g (yield 76.5%) of the compound was obtained per batch. The synthesized CO(15NH2)2 contained 46.2% N, 0.55% biuret, melting point of 132.55 ºC and did not exhibit isotopic fractionation. The production cost of CO(15NH2)2 with 90.0 at. % 15N was US$ 238.60 per gram.

Environmental assessment of residues generated after consecutive acid-base pretreatment of sugarcane bagasse by advanced oxidative process

Abstract Background Biofuels produced from sugarcane bagasse (SB) have shown promising results as a suitable alternative of gasoline. Biofuels provide unique, strategic, environmental and socio-economic benefits. However, production of biofuels from SB has negative impact on environment due to the use of harsh chemicals during pretreatment. Consecutive sulfuric acid-sodium hydroxide pretreatment of SB is an effective process which eventually ameliorates the accessibility of cellulase towards cellulose for the sugars production. Alkaline hydrolysate of SB is black liquor containing high amount of dissolved lignin. Results This work evaluates the environmental impact of residues generated during the consecutive acid-base pretreatment of SB. Advanced oxidative process (AOP) was used based on photo-Fenton reaction mechanism (Fenton Reagent/UV). Experiments were performed in batch mode following factorial design L9 (Taguchi orthogonal array design of experiments), considering the three operation variables: temperature (°C), pH, Fenton Reagent (Fe2+/H2O2) + ultraviolet. Reduction of total phenolics (TP) and total organic carbon (TOC) were responsive variables. Among the tested conditions, experiment 7 (temperature, 35°C; pH, 2.5; Fenton reagent, 144 ml H2O2+153 ml Fe2+; UV, 16W) revealed the maximum reduction in TP (98.65%) and TOC (95.73%). Parameters such as chemical oxygen demand (COD), biochemical oxygen demand (BOD), BOD/COD ratio, color intensity and turbidity also showed a significant change in AOP mediated lignin solution than the native alkaline hydrolysate. Conclusion AOP based on Fenton Reagent/UV reaction mechanism showed efficient removal of TP and TOC from sugarcane bagasse alkaline hydrolysate (lignin solution). To the best of our knowledge, this is the first report on statistical optimization of the removal of TP and TOC from sugarcane bagasse alkaline hydrolysate employing Fenton reagent mediated AOP process.